The ones going to the third 'T' should be the same length to avoid out-of-phase issues.
Joe M. Larry Horlick wrote: > > > I have a drawing from Sinclair that shows 4 stacked folded dipoles (it > does not indicate an > antenna model) using all 50 ohm cable. So using the 210C4 harness > picture from the link > below as a template, this is how it's done: > > Feedlines from dipole A, B, C, and D are any length, but identical. A > and B go to a tee, > C and D go to another tee. The feedlines from the output (if I am > allowed to use that rather > crude term!) of these tees are any odd 1/4 wavelength (but do not have > to be the same) and go > to a 3rd tee. The output of this tee is 50 ohms. I suspect that the > harness does not affect the > pattern, but rather it is the dipole to mast spacing. > > lh > > On 5/18/10, *N1BUG* <[email protected] <mailto:[email protected]>> wrote: > > Hi Burt, > > > Did I hear my name mentioned??? Maybe just ESP:-) > > Yes you did, Great Sinclair dipole guru! :-) > > I got the dipole drawing from your new web site. Thanks! That part > I'm clear on, but still a bit confused on the phasing harness. > > > I would suggest that you don't even consider putting the harnass > inside > > the mast (unless Harold can tell us how Sinclair does it). Put the > > harness on the outside of the mast like the SRL210A4. > > Uh, yeah, I hear that. I like the idea of the internal harness, but > I just spent 3 hours getting the old harness *out* of the mast. I > can't imagine how it was put *in* there. > > > To combine the impedances on a 4 bay Sinclair array is simple. Divide > > the dipoles into pairs and parallel them. This gives 25 ohms. > Then add > > an electrical quarter wave of 50 ohm coax (RG-213/U) to transform > it to > > 100 ohms. Combine the matching coax from each pair in parallel to > give > > 50 ohms. Then you can connect your feedline at any length from this > > latter 50 ohm connection. > > Here is a crude drawing of what I think you are saying: > > http://www.n1bug.com/dipoleharness1.jpg > > Points X and Y are the 100 ohm points created by adding an > electrical quarter wave of RG-213 coming out of the 25 ohm point > where two dipoles are connected in parallel. But points X and Y are > physically several feet apart. That being said, I think the coax > that joins those points at the final parallel junction (to connect > to the feedline) would have to be a multiple of an electrical half > wavelength in order to repeat the 100 ohms at the other end (thus > ending up with 50 ohms when you parallel them)? > > If so, I'm still confused on how they did this for both cardioid and > bidirectional versions of this antenna with the harness inside the > mast. Required physical lengths would be different due to the > different dipole spacing from the mast. One can only work with > physical lengths that "fit" inside the mast (I guess?) but this > seems to clash with the electrical length required for impedance > matching. It's a non-issue since I have no way of getting a new > harness inside the mast. With an external harness I can just coil up > or loop any extra length required for matching reasons. But I'd > still like to understand how they did it. :-) > > In any case, the phasing harness on my 210C4 was done differently. > It uses a combination of RG-213/U and RG-63B/U in the harness > itself. Here is a sketch of it: > > http://www.n1bug.com/210C4harness.jpg > > Here, if we assume points X and Y are 100 ohms, point Z (where the > feedline attaches) would fall somewhere between 50 ohms and 78 ohms, > depending on the electrical length of the RG-63B/U coax connecting > them. I'm trying to look up the velocity factor of RG-63B/U (part > PE, part air dielectric), but having no luck so far. > > All of which seems completely different from the picture at > > http://forum.radioamateur.ca/index.php?topic=2245.0 > > where there appears to be just a quarter wave section of coax off > each side of point Z to the "T" for each pair of dipoles. I don't > know how that was physically possible given the dipole spacing. I > think we can safely assume I'm missing something here. :-) > > Paul N1BUG > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > [email protected] > <mailto:[email protected]> > > > > > >
